Polymerisation process

ABSTRACT

A process for transitioning between two catalysts is disclosed, comprising the steps of a) discontinuing the feed of the first catalyst into the polymerization reactor, and then b) introducing the second catalyst into the reactor, wherein one of the catalysts comprises a late transition metal catalyst and the other is a catalyst which is incompatible therewith. It is preferred that the late transition metal catalyst is a 2,6-diacetyl pyridine iron catalyst.

[0001] The present invention relates to a process for the polymerisationand copolymerisation of 1-olefins, and particularly to a process fortransitioning between different polymerization catalyst systems.

[0002] During the production of olefin polymers in a commercial reactorit is often necessary to transition from one type of catalyst systemproducing polymers having certain properties and characteristics toanother catalyst system capable of producing polymers of differentchemical and/or physical attributes. Transitioning between similartraditional Ziegler-Natta type catalysts for example, or compatiblecatalysts, generally takes place easily. However, where the catalystsare incompatible or of different types the process is typicallycomplicated. For example, transitioning between a traditionalZiegler-Natta type catalyst and chromium based catalyst, twoincompatible catalysts, it has been found that some of the components ofthe traditional Ziegler catalyst or the cocatalyst/activator act aspoisons to the chromium based catalyst. Consequently, these poisonsprevent the chromium catalyst from promoting polymerization. In anotherexample, the extreme different responses to molecular weight regulators,such as hydrogen and comonomer, of traditional Ziegler-Natta catalystsand metallocene catalysts makes these catalysts incompatible. Any tracesof active Ziegler-Natta catalyst will produce very high molecular weightproduct under metallocene catalyst reactor conditions. Furthermore,particularly in a continuous transitioning process, the interactionbetween the two incompatible catalysts may lead to production of highlevels of small particles less than about 100 microns, termed fines.These fines can induce operability problems in the reactor such asfouling and sheeting.

[0003] In known transitioning techniques, to accomplish an effectivetransition between incompatible catalysts, the first catalyzed olefinpolymerization process is stopped by various techniques known in theart. For example in reactions involving use of chromium based catalysts,oxygen, CO, water or polar hydrocarbons such as alcohols, ethers,ketones and aldehydes are known to be effective in reaction termination.The reactor is then emptied, recharged and a second catalyst isintroduced into a reactor. Such catalyst conversions are time consumingand costly because of the need for a reactor shut-down for an extendedperiod of time during transition.

[0004] WO 99/12981 discloses that ethylene and other 1-olefins may bepolymerised by contacting it with certain late transition metalcomplexes of selected 2,6-pyridinecarboxaldehydebis (imines) and2,6-diacylpyridinebis (imines).

[0005] EP-A-75 1965 discloses methods of transitioning betweenincompatible catalysts, involving the use of catalyst killers. Itdefines “incompatible” catalysts as those which satisfy one or more ofthe following criteria: 1) those catalysts that in each other's presencereduce the activity of at least one of the catalysts by greater than50%; 2) those catalysts such that under the same reactive conditions oneof the catalysts produces polymers having a molecular weight greaterthan two times higher than any other catalyst in the system; and 3)those catalysts that differ in comonomer incorporation or reactivityratio under the same conditions by more than about 30%.

[0006] According to the above definition, late transition metalcatalysts such as the above-mentioned2,6-pyridinecarboxaldehydebis(imine) type catalysts are incompatiblewith most known types of catalysts. For example,2,6-pyridinecarboxaldehydebis(imine) type catalysts typically exhibit avery low comonomer incorporation or reactivity ratio compared with othercatalyst types. Accordingly it would be expected that transitioning fromone to the other would require procedures such as those described abovefor incompatible catalysts, with all the attendant disadvantages.

[0007] We have surprisingly discovered however that it is possible totransition between late transition metal catalysts and catalysts whichare incompatible according to the above definition without the need forsuch procedures.

[0008] Accordingly in a first aspect the present invention provides aprocess for the polymerisation and copolymerisation of 1-olefins inwhich a transition is made between two catalysts, comprising the stepsof

[0009] a) discontinuing the feed of the first catalyst into thepolymerization reactor, and then

[0010] b) introducing the second catalyst into the reactor,

[0011] wherein one of the catalysts comprises a late transition metalcatalyst and the other is a catalyst which is incompatible therewith.

[0012] Preferably the transition is effected by introducing the secondcatalyst without first eliminating all activity of the first catalystand/or without first removing all traces of the first catalyst. Morepreferably, no deactivating agent (catalyst killer) is used.

[0013] In an alternative embodiment, subsequent to step a) adeactivating agent in a sufficient amount to deactivate the firstcatalyst is introduced into the reactor before the second catalyst isintroduced into the reactor.

[0014] By “late transition metal catalyst” (hereinafter LTM catalyst) ismeant a catalyst comprising a complex of a metal from Groups VIIIb or Ibof the Periodic Table.

[0015] By “incompatible” is meant the definition previously given:namely that the two catalysts satisfy at least one of the followingconditions: 1) catalysts which in each other's presence reduce theactivity of at least one of the catalysts by greater than 50%; 2) underthe same reactive conditions one of the catalysts produces polymershaving a molecular weight two times or more that of any other catalystin the system; and 3) catalysts that differ in comonomer incorporationor reactivity ratio under the same conditions by more than 30%.

[0016] Catalysts which are incompatible with the LTM catalysts includesPhillips type (chromium) catalysts, metallocene catalysts andZiegler-Natta catalysts. However this invention also includes within itsscope the case where two LTM catalysts are incompatible with each otheraccording to the above definition.

[0017] Preferably the LTM catalyst comprises a complex of the formula

[0018] wherein

[0019] M is Fe[II], Fe[III], Co[II], Co[III], Ni[II], Rh[II], Rh[III],Ru[II], Ru[III], Ru[IV] or Pd[II); X represents an atom or groupcovalently or ionically bonded to the transition metal M; T is theoxidation state of the transition metal M and b is the valency of theatom or group X; L is a group datively bound to M, and n is from 0 to 5;A¹ to A³ are each independently N or P or CR, with the proviso that atleast one is CR; and R⁴ to R⁷ are each independently selected fromhydrogen, halogen, hydrocarbyl, substituted hydrocarbyl,heterohydrocarbyl, substituted heterohydrocarbyl or SiR′₃ where each R′is independently selected from hydrogen, halogen, hydrocarbyl,substituted hydrocarbyl, heterohydrocarbyl and substitutedheterohydrocarbyl.

[0020] A typical Phillips type catalyst employs a combination of asupport material to which has first been added a chromium-containingmaterial wherein at least part of the chromium is in the hexavalentstate by heating in the presence of molecular oxygen. The support isgenerally composed of about 80 to 100 wt. % silica, the remainder, ifany, being selected from the group consisting of refractory metaloxides, such as aluminium, boria, magnesia, thoria, zirconia, titaniaand mixtures of two or more of these refractory metal oxides. Supportscan also comprise alumina, aluminium phosphate, boron phosphate andmixtures thereof with each other or with silica.

[0021] The chromium compound is typically added to the support as achromium (III) compound such as the acetate or acetylacetonate in orderto avoid the toxicity of chromium (VI). The raw catalyst is thencalcined in air at a temperature between 250 and 1000° C. for a periodof from a few seconds to several hours. This converts at least: part ofthe chromium to the hexavalent state. Reduction of the Cr VI to itsactive form normally occurs in the polymerisation reaction, but can bedone at the end of the calcination cycle with CO at about 350° C.

[0022] Fluorine, aluminium and/or titanium may be added to the rawPhillips catalyst to modify it.

[0023] Metallocenes may typically be represented by the general formula:

(C₅R_(n))_(y)Z_(x)(C₅R_(m)) M L_((4−y−1))

[0024] where

[0025] (C₅R_(x))_(n) and (C₅R_(m)) are cyclopentadienyl ligands,

[0026] R is hydrogen, alkyl, aryl, alkenyl, etc.

[0027] M is a Group IVA metal

[0028] Z is a bridging group,

[0029] L is an anionic ligand, and

[0030] y is 0,1 or 2, n and m are from 1 to 5, x is 0 or 1.

[0031] The most preferred complexes are those wherein y is 1 and L ishalide or alkyl. Typical examples of such complexes are bis(cyclopentadienyl) zirconium dichloride and bis(cyclopentadienylzirconium dimethyl. In such metallocene complexes thecyclopentadienyl-ligands may suitably be substituted by alkyl groupssuch as methyl, n-butyl or vinyl. Alternatively the R groups may bejoined together to form a ring substituent, for example indenyl orfluorenyl. The cyclopentadienyl ligands may be the same or different.Typical examples of such complexes are bis(n-butylcyclopentadienyl)zirconium dichloride or bis (methylcyclopentadienyl) zirconiumdichloride.

[0032] Further examples of metallocene complexes are those wherein theanionic ligand represented in the above formula is replaced with a dienemoiety. In such complexes the transition metal may be in the +2 or +4oxidation state and a typical example of this type of complex isethylene bis indenyl zirconium (II) 1,4-diphenyl butadiene. Examples ofsuch complexes may be found in EP 775148A the disclosure of which isincorporated herein by reference.

[0033] Ziegler-Natta catalysts, in general, consist of two maincomponents. One component is an alky or hydride of a Group I to IIImetal, most commonly Al(Et)₃ or Al(iBu)₃ or Al(Et)₂Cl but alsoencompassing Grignard reagents, n-butyllithium, or dialkylzinccompounds. The second component is a salt of a Group IV to VIIItransition metal, most commonly halides of titanium or vanadium such asTiCl_(4,) TiCl₃, VCl₄, or VOCl₃. The catalyst components when mixed,usually in a hydrocarbon solvent, may form a homogeneous orheterogeneous product. Such catalysts may be impregnated on a support,if desired, by means known to those skilled in the art and so used inany of the major processes known for co-ordination catalysis ofpolyolefins such as solution, slurry, and gas-phase. In addition to thetwo major components described above, minor amounts of other compounds(typically electron donors) may be added to further modify thepolymerisation behaviour or activity of the catalyst. A wide variety ofmonomers may thus be polymerised by Ziegler-Natta catalysts. Dependingon the particular components used, and the specific method ofcombination, it is possible to produce catalysts which are veryeffective for the polymerisation and copolymerisation of ethylene,dienes, and higher alpha-olefins. Particularly important applicationsfor Ziegler-Natta catalysts are for the manufacture of high molecularweight ethylene copolymers and isotactic polypropylene.

[0034] It will be understood that the transitioning process of theinvention can be performed in either direction—i.e. from the LTMcatalyst to the other catalyst or vice versa. Furthermore, it will beunderstood that whilst it is not in fact necessary to take any action toaddress the activity/presence of the first catalyst before adding thesecond, it is within the scope of the invention to reduce or eliminatethe activity of the first catalyst and/or to remove at least part of thecatalyst. For example, the activity of the first catalyst may be reducedby up to 30% from its maximum prior to addition of the second catalyst,or alternatively by up to 50, 70 or by at least 95%, or it may be killedcompletely. For reducing activity, known catalyst inhibitors or poisonssuch as oxygen, water, ammonia, carbon monoxide, carbon dioxide,alcohols and ketones may be used. Partial reduction in activity of thefirst catalyst may also for example be achieved by continuingpolymerisation for a certain period of time (for example between 5minutes and 12 hours) after having discontinued introduction of thefirst catalyst and/or any associated co-catalyst, before commencingintroduction of the second catalyst and/or its associated co-catalyst.

[0035] After introduction of the first catalyst has been discontinued,the polymerisation reactor may be partially or completely emptied.Completely emptying the reactor ensures that when the second catalyst isintroduced, all the polymer subsequently produced is purely that derivedfrom the second catalyst. However it is preferred at most only topartially empty the reactor, e.g. by reducing the bed height in the caseof a gas phase fluidised bed reactor, as this is less disruptive of thepolymerisation process. Although this results in the polymerisation withthe second catalyst initially producing polymer which is mixed withpolymer derived from the first catalyst, this is a relatively minorproblem in the case of the present invention, because one of thecatalysts is a late transition metal catalyst. Typically, between zeroand half of the contents of the reactor by volume may be removed, thoughpreferably only one third or less are removed. In the most preferredcase, none of the contents of the reactor are removed prior tocommencing the polymerisation with the second catalyst.

[0036] When transitioning from a first to a second catalyst the usualinitial step is to discontinue the catalyst feed. If desired, thepolymerisation reactor may then be partially or completely emptied, asdiscussed above. The new catalyst is then introduced and, if necessary,the reactor conditions are adapted to the conditions required by the newcatalyst. For example, in the case of transition from a chromiumcatalyst when the reactor is not completely emptied, the transition isfollowed by IR measurements on the produced polymer to determine whenthe system is free from any chromium-based polymer, i.e. to determinewhen the produced polymer is within the LTM polymer specifications. Thetransition can also be followed by melt index measurements of theproduced polymer.

[0037] The specific reactor conditions during transition depend interalia on catalyst activity, type and amount of comonomer, type of polymerto be produced, and the production equipment. Consequently, they have tobe determined for each specific product in a particular plant. Forexample, in general the reactor conditions when using metallocenecatalysts include a reduced feed of comonomer because the comonomers aremuch more readily incorporated in metallocene catalyzed polymers than inLTM catalysed polymers of equal polymer density. The melt flow index iscorrected by introducing hydrogen, and also, to a certain degree,ethylene.

[0038] A particularly favoured transition is that between2,6-pyridinecarboxaldehydebis(imine) type catalysts comprising complexesof the formula (I) as defined above, and chromium catalysts.

[0039] It is preferred that the process of the invention is carried outin slurry or gas phase.

[0040] In the complexes of Formula (I) it is preferred that A¹ to A³ areeach independently CR where each R is as defined above. In alternativepreferred embodiments, A¹ and A³ are both N and A² is CR, or one of A¹to A³ is N and the others are independently CR.

[0041] The group L may be an ether such as tetrahydrofuran ordiethylether, and alcohol such as ethanol or butanol, a primary,secondary or tertiary amine, or a phosphine.

[0042] Preferred catalysts based on complexes of the Formula (I)comprise a complex having the formula

[0043] wherein

[0044] R¹ to R⁷ are each independently selected from-hydrogen, halogen,hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl, substitutedheterohydrocarbyl or SiR′₃ where each R′ is independently selected fromhydrogen, halogen, hydrocarbyl, substituted hydrocarbyl,heterohydrocarbyl, substituted heterohydrocarbyl.

[0045] R⁵ and R⁷ are preferably independently selected from substitutedor unsubstituted alicyclic, heterocyclic or aromatic groups, forexample, phenyl, 1-naphthyl, 2-naphthyl, 2-methylphenyl, 2-ethylphenyl,2,6-diisopropylphenyl, 2,3-diisopropylphenyl, 2,4-diisopropylphenyl,2,6-di-n-butylphenyl, 2,6-dimethylphenyl, 2,3-dimethylphenyl,2,4-dimethylphenyl, 2-t-butylphenyl, 2,6-diphenylphenyl,2,4,6-trimethylphenyl, 2,6-trifluoromethylphenyl,4-bromo-2,6-dimethylphenyl, 3,5 dichloro2,6-diethylphenyl, and2,6,bis(2,6-dimethylphenyl)phenyl, cyclohexyl and pyridinyl.

[0046] In a preferred embodiment R⁵ is represented by the group “P” andR⁷ is represented by the group “Q” as follows:

[0047] wherein

[0048] R¹⁹ to R²⁸ are independently selected from hydrogen, halogen,hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl or substitutedheterohydrocarbyl; when any two or more of R¹ to R⁴, R⁶ and R¹⁹ to R²⁸are hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl orsubstituted heterohydrocarbyl, said two or more can be linked to formone or more cyclic substituents.

[0049] The ring systems P and Q are preferably independently2,6-hydrocarbylphenyl or fused-ring polyaromatic, for example,1-naphthyl, 2-naphthyl, 1-phenanthrenyl and 8-quinolinyl.

[0050] Preferably at least one of R¹⁹, R²⁰, R²¹ and R²² is hydrocarbyl,substituted hydrocarbyl, heterohydrocarbyl or substitutedheterohydrocarbyl. More preferably at least one of R¹⁹ and R²⁰, and atleast one of R²¹ and R²², is hydrocarbyl, substituted hydrocarbyl,heterohydrocarbyl or substituted heterohydrocarbyl. Most preferably R¹⁹,R^(20,) R²¹ and R²² are all independently selected from hydrocarbyl,substituted hydrocarbyl, heterohydrocarbyl or substitutedheterohydrocarbyl. R¹⁹, R²⁰, R²¹and R²² are preferably independentlyselected from methyl, ethyl, n-propyl, iso-propyl, n-butyl, sec-butyl,tert.-butyl, n-pentyl, neopentyl, n-hexyl, 4-methylpentyl, n-octyl,phenyl and benzyl.

[0051] R¹, R², R³, R⁴, R⁶, R¹⁹, R²⁰, R²¹, R²², R²³, R²⁵, R²⁶ and R²⁸ arepreferably independently selected from hydrogen and C₁ to C₈hydrocarbyl, for example, methyl, ethyl, n-propyl, n-butyl, t-butyl,n-hexyl, n-octyl, phenyl and benzyl.

[0052] In an alternative embodiment R⁵ is a group having the formula—NR²⁹R³⁰ and R⁷ is a group having the formula —NR³¹R³², wherein R²⁹ toR³² are independently selected from hydrogen, halogen, hydrocarbyl,substituted hydrocarbyl, heterohydrocarbyl or substitutedheterohydrocarbyl; when any two or more of R¹ to R⁴, R⁶ and R²⁹ to R³²are hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl orsubstituted heterohydrocarbyl, said two or more can be linked to formone or more cyclic substituents.

[0053] Each of the atoms nitrogen atoms is coordinated to the metal by a“dative” bond, ie a bond formed by donation of a lone pair of electronsfrom the nitrogen atom. The remaining bonds on each of these atoms arecovalent bonds formed by electron sharing between the atoms and theorganic ligand as shown in the defined formula for the metal complexillustrated above.

[0054] The atom or group represented by X in the compounds of Formula(I) and (II) can be, for example, selected from halide, sulphate,nitrate, thiolate, thiocarboxylate, BF₄ ⁻, PF₆ ⁻, hydride,hydrocarbyloxide, carboxylate, hydrocarbyl, substituted hydrocarbyl andheterohydrocarbyl, or β-diketonates. Examples of such atoms or groupsare chloride, bromide, methyl, ethyl, propyl, butyl, octyl, decyl,phenyl, benzyl, methoxide, ethoxide, isopropoxide, tosylate, triflate,formate, acetate, phenoxide and benzoate. Preferred examples of the atomor group X in the compounds of Formula (I) are halide, for example,chloride, bromide; hydride; hydrocarbyloxide, for example, methoxide,ethoxide, isopropoxide, phenoxide; carboxylate, for example, formate,acetate, benzoate; hydrocarbyl, for example, methylethyl, propyl, butyl,octyl, decyl, phenyl, benzyl; substituted hydrocarbyl;heterohydrocarbyl; tosylate; and triflate. Preferably X is selected fromhalide, hydride and hydrocarbyl. Chloride is particularly preferred.

[0055] Preferred metals M in the complexes of Formula (I) are Fe and Co.

[0056] Preferred compounds of the Formula (I) include the following:

[0057] 2,6-diacetylpyridinebis(2,6-diisopropylanil)FeCl₂

[0058] 2,6-diacetylpyridine(2,6-diisopropylanil)CoCl₂

[0059] 2,6-diacetylpyridinebis(2-tert.-butylanil)FeCl₂

[0060] 2,6-diacetylpyridinebis(2,3-dimethylanil)FeCl₂

[0061] 2,6-diacetylpyridinebis(2-methylanil)FeCl₂

[0062] 2,6-diacetylpyridinebis(2,4-dimethylanil)FeCl₂

[0063] 2,6-diacetylpyridinebis(2,6-dimethylanil)FeCl₂

[0064] 2,6-diacetylpyridinebis(2,4,6 trimethyl anil)FeCl₂

[0065] 2,6-dialdiminepyridinebis(2,6-dimethylanil)FeCl₂

[0066] 2,6-dialdiminepytidinebis(2,6-diethylanil)FeCl₂

[0067] 2,6-dialdiminepyridinebis(2,6-diisopropylanil)FeCl₂

[0068] 2,6dialdiminepyridinebis(1-naphthil)FeCl₂ or

[0069] 2,6-bis(1,1-diphenylhydrazone)pyridine FeCl₂.

[0070] Each of the catalysts utilised in the present invention can ifdesired comprise more than one compound of that type. For example, thecatalysts of Formula (I) can also include one or more other types oftransition metal compounds or catalysts, for example, nitrogencontaining catalysts such as those described in our copendingapplications WO 99/12981 or GB 9903402.7.

[0071] The complexes of formula (I) are generally used as catalysts inconjunction with activator compounds. Examples of such activatorcompounds include organoaluminium compounds and hydrocarbylboroncompounds. Suitable organoaluminium compounds include compounds of theformula AlR₃, where each R is independently C₁-C₁₂ alkyl or halo.Examples include trimethylaluminium (TMA), triethylaluminium (TEA),tri-isobutylaluminium (TIBA), tri-n-octylaluminium, methylaluminiumdichloride, ethylaluminium dichloride, dimethylaluminium chloride,diethylaluminium chloride, ethylaluminiumsesquichloride,methylaluminiumsesquichloride, and alumoxanes. Alumoxanes are well knownin the art as typically the oligomeric compounds which can be preparedby the controlled addition of water to an alkylaluminium compound, forexample trimethylaluminium. Such compounds can be linear, cyclic ormixtures thereof. Commercially available alumoxanes are generallybelieved to be mixtures of linear and cyclic compounds. The cyclicalumoxanes can be represented by the formula [R¹⁶AlO]_(s) and the linearalumoxanes by the formula R¹⁷(R¹⁸AlO)_(s) wherein s is a number fromabout 2 to 50, and wherein R¹⁶, R¹⁷, and R¹⁸ represent hydrocarbylgroups, preferably C₁ to C₆ alkyl groups, for example methyl, ethyl orbutyl groups. Alkylalumoxanes such as methylalumoxane (MAO) arepreferred.

[0072] Mixtures of alkylalumoxanes and trialkylaluminium compounds areparticularly preferred, such as MAO with TMA or TIBA. In this context itshould be noted that the term “alkylalumoxane” as used in thisspecification includes alkylalumoxanes available commercially which maycontain a proportion, typically about 10 wt %, but optionally up to 50wt %, of the corresponding trialkylalurninium; for instance, commercialMAO usually contains approximately 10 wt % trimethylaluminium (TMA),whilst commercial MMAO contains both TMA and TIBA. Quantities ofalkylalumoxane quoted herein include such trialkylaluminium impurities,and accordingly quantities of trialkylaluminium compounds quoted hereinare considered to comprise compounds of the formula AlR₃ additional toany AlR₃ compound incorporated within the alkylalumoxane when present.

[0073] Examples of suitable hydrocarbylboron compounds are boroxines,trimethylboron, triethylboron,dimethylphenylammoniumtetra(phenyl)borate, trityltetra(phenyl)borate,triphenylboron, dimethylphenylammonium tetra(pentafluorophenyl)borate,sodium tetrakis[(bis-3,5-trifluoromethyl)phenyl]borate,H⁺(OEt₂)[(bis-3,5-trifluoromethyl)phenyl]borate,trityltetra(pentafluorophenyl)borate and tris(pentafluorophenyl) boron.

[0074] An alternative class of activators comprise salts of a cationicoxidising agent and a non-coordinating compatible anion. Examples ofcationic oxidising agents include: ferrocenium, hydrocarbyl-substitutedferrocenium, Ag⁺, or Pb²⁺. Examples of non-coordinating compatibleanions are BF₄ ⁻, SbF₆ ⁻, PF₆ ⁻, tetrakis(phenyl)borate andtetrakis(pentafluorophenyl)borate.

[0075] The catalysts utilised in the present invention can beunsupported or supported on a support material, for example, silica,alumina, MgCl₂ or zirconia, or on a polymer or prepolymer, for examplepolyethylene, polypropylene, polystyrene, or poly(aminostyrene).

[0076] The polymerisation conditions can be, for example, solutionphase, slurry phase, gas phase or bulk phase, with polymerisationtemperatures ranging from −100° C. to +300° C., and at pressures ofatmospheric and above, particularly from 140 to 4100 kPa. If desired,the catalyst can be used to polymerise ethylene under high pressure/hightemperature process conditions wherein the polymeric material forms as amelt in supercritical ethylene. Preferably the polymerisation isconducted under gas phase fluidised bed or stirred bed conditions.

[0077] Suitable monomers for use in the polymerisation process of thepresent invention are, for example, ethylene and C₂₋₂₀ α-olefins,specifically propylene, 1-butene, 1-pentene, 1-hexene,4-methylpentene-1, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-undecene,1-dodecene, 1-tridecene, 1-tetradecene, 1-pentadecene, 1-hexadecene,1-heptadecene, 1-octadecene, 1-nonadecene, and 1-eicosene. Othermonomers include methyl methacrylate, methyl acrylate, butyl acrylate,acrylonitrile, vinyl acetate, and styrene. Preferred monomers forhomopolymerisation processes are ethylene and propylene.

[0078] The process of the invention can also be used for copolymerisingethylene or propylene with each other or with other 1-olefins such as1-butene, 1-hexene, 4-methylpentene-1, and octene, or with othermonomeric materials, for example, methyl methacrylate, methyl acrylate,butyl acrylate, acrylonitrile, vinyl acetate, and styrene.

[0079] Irrespective of the polymerisation or copolymerisation techniqueemployed, polymerisation or copolymerisation is typically carried outunder conditions that substantially exclude oxygen, water, and othermaterials that act as catalyst poisons. Also, polymerisation orcopolymerisation can be carried out in the presence of additives tocontrol polymer or copolymer molecular weights.

[0080] Slurry phase polymerisation conditions or gas phasepolymerisation conditions are particularly useful for the production ofhigh or low density grades of polyethylene, and polypropylene. In theseprocesses the polymerisation conditions can be batch, continuous orsemi-continuous. Furthermore, one or more reactors may be used, e.g.from two to five reactors in series. Different reaction conditions, suchas different temperatures or hydrogen or comonomer concentrations may beemployed in the different reactors. In the slurry phase process and thegas phase process, the catalyst is generally metered and transferredinto the polymerisation zone in the form of a particulate solid eitheras a dry powder (e.g. with an inert gas) or as a slurry. This solid canbe, for example, a solid catalyst system formed from the one or more ofcomplexes of the invention and an activator with or without other typesof catalysts, or can be the solid catalyst alone with or without othertypes of catalysts. In the latter situation, the activator can be fed tothe polymerisation zone, for example as a solution, separately from ortogether with the solid catalyst. Preferably the catalyst system or thetransition metal complex component of the catalyst system employed inthe slurry polymerisation and gas phase polymerisation is supported onone or more support materials. Most preferably the catalyst system issupported on the support material prior to its introduction into thepolymerisation zone. Suitable support materials are, for example,silica, alumina, zirconia, talc, kieselguhr, or magnesia. Impregnationof the support material can be carried out by conventional techniques,for example, by forming a solution or suspension of the catalystcomponents in a suitable diluent or solvent, and slurrying the supportmaterial therewith. The support material thus impregnated with catalystcan then be separated from the diluent for example, by filtration orevaporation techniques. Once the polymer product is discharged from thereactor, any associated and absorbed hydrocarbons are substantiallyremoved, or degassed, from the polymer by, for example, pressurelet-down or gas purging using fresh or recycled steam, nitrogen or lighthydrocarbons (such as ethylene). Recovered gaseous or liquidhydrocarbons may be recycled to the polymerisation zone.

[0081] In the slurry phase polymerisation process the solid particles ofcatalyst, or supported catalyst, are fed to a polymerisation zone eitheras dry powder or as a slurry in the polymerisation diluent. Thepolymerisation diluent is compatible with the polymer(s) andcatalyst(s), and may be an alkane such as hexane, heptane, isobutane, ora mixture of hydrocarbons or paraffins. Preferably the particles are fedto a polymerisation zone as a suspension in the polymerisation diluent.The polymerisation zone can be, for example, an autoclave or similarreaction vessel, or a continuous loop reactor, e.g. of the typewell-know in the manufacture of polyethylene by the Phillips Process.When the polymerisation process of the present invention is carried outunder slurry conditions the polymerisation is preferably carried out ata temperature above 0° C., most preferably above 15° C. Thepolymerisation temperature is preferably maintained below thetemperature at which the polymer commences to soften or sinter in thepresence of the polymerisation diluent. If the temperature is allowed togo above the latter temperature, fouling of the reactor can occur.Adjustment of the polymerisation within these defined temperature rangescan provide a useful means of controlling the average molecular weightof the produced polymer. A further useful means of controlling themolecular weight is to conduct the polymerisation in the presence ofhydrogen gas which acts as chain transfer agent. Generally, the higherthe concentration of hydrogen employed, the lower the average molecularweight of the produced polymer.

[0082] In bulk polymerisation processes, liquid monomer such aspropylene is used as the polymerisation medium.

[0083] Methods for operating gas phase polymerisation processes are wellknown in the art. Such methods generally involve agitating (e.g. bystirring, vibrating or fluidising) a bed of catalyst, or a bed of thetarget polymer (i.e. polymer having the same or similar physicalproperties to that which it is desired to make in the polymerisationprocess) containing a catalyst, and feeding thereto a stream of monomerat least partially in the gaseous phase, under conditions such that atleast part of the monomer polymerises in contact with the catalyst inthe bed. The bed is generally cooled by the addition of cool gas (e.g.recycled gaseous monomer) and/or volatile liquid (e.g. a volatile inerthydrocarbon, or gaseous monomer which has been condensed to form aliquid). The polymer produced in, and isolated from, gas phase processesforms directly a solid in the polymerisation zone and is free from, orsubstantially free from liquid. As is well known to those skilled in theart, if any liquid is allowed to enter the polymerisation zone of a gasphase polymerisation process the quantity of liquid in thepolymerisation zone is small in relation to the quantity of polymerpresent. This is in contrast to “solution phase” processes wherein thepolymer is formed dissolved in a solvent, and “slurry phase” processeswherein the polymer forms as a suspension in a liquid diluent.

[0084] The gas phase process can be operated under batch, semi-batch, orso-called “continuous” conditions. It is preferred to operate underconditions such that monomer is continuously recycled to an agitatedpolymerisation zone containing polymerisation catalyst, make-up monomerbeing provided to replace polymerised monomer, and continuously orintermittently withdrawing produced polymer from the polymerisation zoneat a rate comparable to the rate of formation of the polymer, freshcatalyst being added to the polymerisation zone to replace the catalystwithdrawn form the polymerisation zone with the produced polymer.

[0085] Methods for operating gas phase fluidised bed processes formaking polyethylene, ethylene copolymers and polypropylene are wellknown in the art. The process can be operated, for example, in avertical cylindrical reactor equipped with a perforated distributionplate to support the bed and to distribute the incoming fluidising gasstream through the bed. The fluidising gas circulating through the bedserves to remove the heat of polymerisation from the bed and to supplymonomer for polymerisation in the bed. Thus the fluidising gas generallycomprises the monomer(s) normally together with some inert gas (e.g.nitrogen or inert hydrocarbons such as methane, ethane, propane, butane,pentane or hexane) and optionally with hydrogen as molecular weightmodifier. The hot fluidising gas emerging from the top of the bed is ledoptionally through a velocity reduction zone (this can be a cylindricalportion of the reactor having a wider diameter) and, if desired, acyclone and or filters to disentrain fine solid particles from the gasstream. The hot gas is then led to a heat exchanger to remove at leastpart of the heat of polymerisation. Catalyst is preferably fedcontinuously or at regular intervals to the bed. At start up of theprocess, the bed comprises fluidisable polymer which is preferablysimilar to the target polymer. Polymer is produced continuously withinthe bed by the polymerisation of the monomer(s). Preferably means areprovided to discharge polymer from the bed continuously or at regularintervals to maintain the fluidised bed at the desired height. Theprocess is generally operated at relatively low pressure, for example,at 10 to 50 bars, and at temperatures for example, between 50 and 120°C. The temperature of the bed is maintained below the sinteringtemperature of the fluidised polymer to avoid problems of agglomeration.

[0086] When using the catalysts of the present invention under gas phasepolymerisation conditions, the catalyst, or one or more of thecomponents employed to form the catalyst can, for example, be introducedinto the polymerisation reaction zone in liquid form, for example, as asolution in an inert liquid diluent. Thus, for example, the transitionmetal component, or the activator component, or both of these componentscan be dissolved or slurried in a liquid diluent and fed to thepolymerisation zone. Under these circumstances it is preferred theliquid containing the component(s) is sprayed as fine droplets into thepolymerisation zone. The droplet diameter is preferably within the range1 to 1000 microns. EP-A-0593083, the teaching of which is herebyincorporated into this specification, discloses a process forintroducing a polymerisation catalyst into a gas phase polymerisation.The methods disclosed in EP-A-0593083 can be suitably employed in thepolymerisation process of the present invention if desired.

[0087] The present invention is illustrated in the following Examples.The two catalysts used are incompatible according to category 2) of thepreviously mentioned definition, in that they have substantiallydiffering HLMI.

EXAMPLES Example 1a Preparation of 2,6-diacetylpyridinebis (2,4,6trimethyl anil) FeCl₂ Supported on Silica (Catalyst 1)

[0088] Catalyst 1 was made as described in detail in WO 99/46304,incorporated herein by reference. The silica support was preimpregnatedwith MAO (methylaluminoxane).

Example 1b Preparation of Chromium Catalyst (Catalyst 2)

[0089] A silica supported chromium catalyst, Grace Sylopol HA30W,typical surface area 500 m²/g and 1.5 ml/g pore volume, containing 1%chromium, was activated by heating in dry air within a fluidised bed.700 g of catalyst was fluidised at 30 mm/sec air velocity. Activationtemperature was ramped at 100° C./hour to a hold temperature of 650° C.,which was then maintained for 5 hours. The catalyst was then cooledunder air fluidisation to 325° C., then fluidised in dry nitrogen duringcooling to ambient temperature. The activated catalyst was stored undera dry nitrogen atmosphere prior to use.

Example 1c Pilot Scale Process Operation Transitioning BetweenPyridinecarboxaldehydebis(imine) Type Catalyst and Phillips Catalyst

[0090] A 93 litre Phillips continuous polymerisation loop reactor wasused for the polymerisations. Ethylene, isobutane diluent, hydrogen andcatalyst were metered into the reactor to maintain the reactionconditions as detailed in Table 1 below. The reactor incorporated twoseparate catalyst feeder systems, which enabled storage of theindividual catalysts as isobutane slurries. A pressurised meteringsystem was employed to control addition of either to the reactor.Catalysts 1 and 2 were charged separately to each feeder system. Thereactor was operated at 600 psig and 90° C. with a polyethylenethroughput of 6.8-7.6 kg/hour.

[0091] Reaction conditions were established to demonstrate the catalystproductivity and basic polymer properties obtained in use of thePhillips catalyst (Catalyst 2, Condition 1). Subsequently, from a cleanreactor startup, process conditions and polymer properties wereestablished from use of Catalyst 1 (Condition 2). A transition fromCatalyst 1 to Catalyst 2 was then made by simply switching betweencatalyst supply feeders, without alteration of reaction conditions norany addition of reaction kill agents, nor flushing of reactor contents(Condition 3). Reaction conditions were maintained to demonstrate theattainment of the predetermined process conditions and polymerproperties established under Condition 1.

[0092] A similar transition was then made to return to Catalyst 1, againwithout deliberate poison addition or flushing of reactor contents(Condition 4). The results summarised in the attached table and inFIG. 1. TABLE 1 Condition 1 2 3 4 Catalyst 2 1 2 1 Reference StartupTransition Transition 1 2 Temperature (° C.) 90 90 90 90 CatalystProductivity (g/g) 6497 7090 8043 8193 Solids (wt %) 30.0 29.8 32.5 24.2Ethylene (vol %) 10.4 13.2 14.6 13.5 Hydrogen (vol %) 0.34 0.26 0.330.26 Ethylene feed kg/h 7.6 7.6 7.3 6.8 Residence time (hours) 1.96 1.892.0 1.75 Product: HLMI (21.6 kg: g/10 mins) 1.27 13.1 1.19 9.4

Example 2a Preparation of 2,6-diacetylpyridinebis (2,4,6 trimethyl anil)FeCl₂ Supported on Silica (Catalyst 3) Catalyst 1 was made as describedin detail in WO 99/46304, incorporated herein by reference. The silicasupport was preimpregnated with MAO (methylaluminoxane). Example 2bPreparation of Chromium Catalyst (Catalyst 4)

[0093] Into a fluidized bed reactor heated at 30° C. and supplied with afluidisation gas composed of nitrogen containing less than 2 vpm ofwater vapour and with a flow rate of 4.7 ml/s, were charged 15 kg of agranular chromium catalyst sold under the trade name EP30XA by IneosSilicas (Warrington, England). The characteristics of this catalyst are:surface area=320 m²/g, pore volume=1.7 ml/g and chromium content=0.25%by weight. Next the reactor was heated from 60° C. to 150° C. at a rateof 100° C./h. The catalyst was then maintained at 150° C. for 30 minutesin the fluidised state. Next 12.5 moles of a mixture of isopropyltitanate and n-butyl titanate sold under the trade name “Tilcom BIP” byTitanium Intermediates Limited (Billingham, England) were introducedinto the reactor. The reactor was then maintained at 150° C. for 2hours. The reactor was then heated from 150° C. to 300° C. at a rate of100° C./h.

[0094] Next the fluidisation by dry nitrogen was changed to fluidisationby dry air. The catalyst was heated to 815° C. at 100° C./h and thenmaintained at 815° C. for 5 hr in the fluidised state. Next the catalystwas cooled to 300° C. at 100° C./h. The fluidisation by dry air was thenchanged to fluidisation by dry nitrogen, and the catalyst cooled to roomtemperature and stored under dry nitrogen.

Example 2c Pilot Scale Process Operation Transitioning Betweenpyridinecarboxaldehydebis(imine) Type Catalyst and Phillips Catalyst

[0095] A fluidised bed reactor 74 cm in diameter was used for thepolymerisations. This contained a fluidized bed and was operated at 90°C. using Catalyst 3. The gas phase was composed of hydrogen, nitrogen,ethylene and hexane fluidised at 42 cm/sec. The partial pressures of thecomponents of the gas mixture are given in Condition 1 of Table 2 below.

[0096] At the start of the transition the injections of Catalyst 3 werestopped, the gas phase maintained in Condition 1 and the reactiondeactivated until the ethylene feed to the reactor had fallen to lessthan 15 kg/hr. At this point feeds to the reactor were stopped. Noreactor kill agents were added.

[0097] The gas phase was purged with nitrogen and the fluidized bedlowered to a height of 3 m. A new gas phase of hydrogen, nitrogen,ethylene and pentane was then established with the values given inCondition 2 of Table 2.

[0098] Chromium catalyst injections using Catalyst 4 manufactured asdescribed above were started at 15 injections per hour and an antistaticagent feed started. Ethylene was fed to the reactor to maintain theethylene partial pressure in the range 5-7 bar, with the hydrogen toethylene partial pressure ratio maintained at 0.36.

[0099] Once reaction was established the catalyst injection ratio wasincreased by +1 injection/hr whilst adjusting the ethylene feed tomaintain an ethylene partial pressure in the reactor of 5-7 bar. Whenthe reactor bed height reached 5 m, product withdrawal was started andfluidisation gas velocity in the reactor increased to 42 cm/s. Afterthree bed renewals the reaction temperature was increased to 105° C. at1° C./hr and the hydrogen partial pressure increased to 3 bar. Thereaction was stabilized at 100 kg/hr at the operating conditions givenin Condition 3 of Table 2. TABLE 2 Condition Condition ConditionParameter Units 1 2 3 Temperature ° C. 90 90 105 Reactor pressure barg20 20 20 Ethylene partial bar 10 6 6 pressure Fluidising velocity cm/s42 37 40 Fluidised bed height m 5 3 5 H₂/C₂ pressure ratio 0.2 0.36660.5 Hydrogen partial b 2 2 3 pressure Hexane partial bar 0.8 0 0pressure Pentane partial bar 0 2 2 pressure Antistatic agent flow ppm 02 2 rate with respect to ethylene feed Product: Non-annealed density 961958 MI HLMI 12.2 MI (2.16 kg) 0.9

[0100] The above results show how a smooth transition between catalystswas possible without the need for the addition of catalyst killers.

1. Process for the polymerisation or copolymerisation of 1-olefins inwhich a transition is made from polymerisation using a first catalyst topolymerisation using a second catalyst, comprising the steps of a)discontinuing the feed of the first catalyst into the polymerisationreactor in which polymerisation with said first catalyst has beenoccurring, and then b) introducing the second catalyst into the reactor,wherein one of the catalysts comprises a late transition metal catalystand the other is a catalyst which is incompatible therewith.
 2. Processaccording to claim 1, wherein before introduction of the secondcatalyst, between zero and half of the contents of the polymerisationreactor by volume are removed.
 3. Process according to claim 2, whereinnone of the contents of the polymerisation reactor by volume are removedbefore introduction of the second catalyst.
 4. Process according to anypreceding claim, wherein the transition is effected by introducing thesecond catalyst without first eliminating all activity of the firstcatalyst and/or without first removing all traces of the first catalyst.5. Process according to any of claims 1 to 3, wherein subsequent to stepa) a deactivating agent in a sufficient amount to deactivate the firstcatalyst is introduced into the reactor before the second catalyst isintroduced into the reactor.
 6. Process according to claim 5, whereinthe activity of the first catalyst is reduced by up to 50% from itsmaximum prior to addition of the second catalyst, or alternatively by50, 70 or 95%, or it may be killed completely.
 7. Process according toclaim 5, wherein the activity of the first catalyst is reduced by atleast 95% from its maximum prior to addition of the second catalyst. 8.Process according to any preceding claim, wherein the late transitionmetal catalyst comprises a complex of the formula

wherein M is Fe[II], Fe[III], Co[II], Co[III], Ni[II], Rh[II], Rh[III],Ru[II], Ru[III], Ru[IV] or Pd[Il]; X represents an atom or groupcovalently or ionically bonded to the transition metal M; T is theoxidation state of the transition metal M and b is the valency of theatom or group X; L is a group datively bound to M, and n is from 0 to 5;A¹ to A³ are each independently N or P or CR, with the proviso that atleast one is CR; and R⁴ to R⁷ are each independently selected fromhydrogen, halogen, hydrocarbyl, substituted hydrocarbyl,heterohydrocarbyl, substituted heterohydrocarbyl or SiR′₃ where each R′is independently selected from hydrogen, halogen, hydrocarbyl,substituted hydrocarbyl, heterohydrocarbyl and substitutedheterohydrocarbyl.
 9. Process according to claim 8 wherein the complexof Formula (I) has the formula

wherein R¹ to R⁷ are each independently selected from hydrogen, halogen,hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl, substitutedheterohydrocarbyl or SiR′₃ where each R′ is independently selected fromhydrogen, halogen, hydrocarbyl, substituted hydrocarbyl,heterohydrocarbyl, substituted heterohydrocarbyl.
 10. Process accordingto claim 9 wherein R⁵ is represented by the group “P” and R⁷ isrepresented by the group “Q” as follows:

wherein R¹⁹ to R²⁸ are independently selected from hydrogen, halogen,hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl or substitutedheterohydrocarbyl; when any two or more of R¹ to R⁴, R⁶ and R¹⁹ to R²⁸are hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl orsubstituted heterohydrocarbyl, said two or more can be linked to formone or more cyclic substituents.
 11. Compound according to any one ofclaims 8 to 10, wherein the late transition metal compound comprises oneof the following: 2,6-diacetylpyridinebis(2,6-diisopropylanil)FeCl₂2,6-diacetylpyridine(2,6-diisopropylanil)CoCl₂2,6-diacetylpyridinebis(2-tert.-butylanil)FeCl₂2,6-diacetylpyridinebis(2,3-dimethylanil)FeCl₂2,6-diacetylpyridinebis(2-methylanil)FeCl₂2,6-diacetylpyridinebis(2,4-dimethylanil)FeCl₂2,6-diacetylpyridinebis(2,6-dimethylanil)FeCl₂2,6-diacetylpyridinebis(2,4,6 trimethyl anil)FeCl₂2,6-dialdiminepyridinebis(2,6-dimethylanil)FeCl₂2,6-dialdiminepyridinebis(2,6-diethylanil)FeCl₂2,6-dialdiminepyridinebis(2,6-diisopropylanil)FeCl₂2,6-dialdiminepyridinebis(1-naphthil)FeCl₂ or2,6-bis(1,1-diphenylhydrazone)pyridine FeCl₂.
 12. Compound according toany preceding claim wherein the non late transition metal catalystcomprises a Phillips type (chromium) catalyst.
 13. Process according toany preceding claim, wherein the conditions are slurry phase or gasphase.